The present invention relates generally to improvements in apparatus for effecting hydrocleaning of the exterior surfaces of pipelines and the like, including pipeline sections, so as to remove coatings and miscellaneous contaminants from the pipeline exterior surface.
As described in the above-noted patent applications, oil and gas transmission pipelines of large diameter (e.g. 12 inches-60 inches) are usually coated and then buried before being used for transportation of fluid. The coatings serve to reduce corrosion caused by the various soils and weathering conditions encountered. Various forms of coating materials have been used over the years. Coal tar products were and are well known as coating materials and, more recently, polyethylene tape layered coatings have been used. However, over the years, these coatings have deteriorated in many instances and several pipeline operators have experienced failures in old coatings. These failures usually involve debonding between parts of the coating and the pipe. Despite the use of cathodic protection, the debonded areas are subject to pitting corrosion and to stress corrosion cracking and in very severe cases pipe failures have occurred under pressure. As a result, many operators have initiated coating rehabilitation projects.
The preferred form of apparatus described in the above-noted earlier patent applications incorporated a main frame adapted to at least partially surround a portion of a pipeline and suitable means for advancing the frame relative to the pipeline in the lengthwise direction when in use. A multiplicity of liquid jetting modules were mounted to the frame in circumferentially spaced relation to each other so as to substantially surround the pipeline when in use. Each such module included a rotary swing arm nozzle thereon having a rotation axis, in use, disposed substantially normal to the pipeline surface for directing liquid jets onto the pipeline surface in a series of closely spaced overlapping convolutions during movement of the frame relative to and lengthwise of the pipeline. Suitable guides, e.g. guide wheels located on each module, made contact with the pipeline surface during movement relative thereto. Suitable suspension linkages connected each module to the frame and a biasing arrangement was provided for urging the respective modules toward the pipeline surface while permitting independent movement of the modules relative to the frame and to one another radially inwardly and outwardly relative to the pipeline as the respective guides contacted and followed the pipeline surface when in use.
The frame configuration for the above-noted hydrocleaner typically included an upper section shaped to surround an upper portion of the pipeline when in use and a pair of lower frame sections pivotally mounted to lower opposed extremities of the upper section for movement between open and closed positions. When the lower sections were in the open position the frame could be lowered downwardly onto the pipeline and the lower sections thereafter closed around the lower portion of the pipeline so that the frame at least partially surrounded the pipeline. Certain of the liquid jetting modules were mounted to the upper frame section while others were mounted to the respective pivotal frame sections. Drive wheels were mounted to the upper frame section for engaging the pipeline surface and advancing the frame relative to the pipeline while the lower frame sections were provided with idler wheels and/or further drive wheels which acted generally in opposition to the drive wheels on the upper frame section thereby to help provide the required tractive forces. An actuator system for pivoting the lower frame sections was provided with suitable biasing means thereby to ensure that the lower idler and/or drive wheels were kept in close pressurized engagement with the pipeline surface so as to provide the required tractive force.
Although the above-described arrangement was found to work quite well, problems were noticed in respect of certain major pipeline variations and deviations from the normal. These deviations involved "out of roundness" of the pipe (usually caused by bending of the pipe); excessively thick coal tar coatings (possibly up to three inches in some sections) along the line and, in some areas, varying thicknesses of coatings around the pipe's circumference especially toward the bottom and, finally, wrinkles in the pipeline surface particularly in the region of bends.
When the above-described hydrocleaning apparatus was used to treat pipeline portions having any or all of the above conditions, certain problems became evident. Many of the problems arose because the above-referred to pivotally mounted lower frame sections would move inwardly and outwardly relative to the center of the pipeline as the wheels thereon followed the pipeline surface. The drive wheels on the upper frame section would of course be in firm contact with upper surface portions of the pipeline at all times as well. Hence, when irregularities of the type noted above were encountered, the lower frame sections would pivot slightly relative to the upper frame section thus varying the relative orientations between the suspension linkages for the liquid jetting modules mounted on the upper frame section and the suspension linkages for those mounted on the lower frame sections. This was found to give rise to losses in cleaning efficiencies for several reasons. Firstly, it will be realized, particularly after a review of the disclosures of the above-noted copending applications, that for maximum efficiency the rotation axis for each of the rotary swing arm nozzle assemblies should pass directly through the pipeline axis. However, once the relative positions of the module suspension linkages had been altered by virtue of the pipeline irregularities noted above, the rotation axes for certain of the swing arms could no longer pass through the pipeline axis. The distances the water jets had to travel from the respective nozzles of the swing arm assemblies to the pipeline surface (referred to as the side standoff distances in the above-noted patent applications) were no longer equal to each other thus causing a loss in cleaning efficiency. Furthermore, although the diameters of the rotary swing arm nozzle assemblies were originally chosen such that the cleaning paths swept out by same would overlap at least slightly on the pipeline surface under normal conditions, the irregular conditions noted above and the resulting changes in the relative orientations around the pipeline surface could in certain cases cause this overlap to be lost with the result being that longitudinally extending streaks of unremoved coating were left on the pipe. While an increase in swing arm length might have been of assistance in some cases, it had to be kept in mind that in many cases, for example a machine having five swing arm assemblies, that the amount of permissible increase in swing arm length was very limited due to the possibility of one swing arm contacting an adjacent one during operation.
In order to alleviate the problem noted above, the present invention in one aspect provides a modified frame arrangement wherein the above-noted lower frame sections each include a pair of independently pivotable frame portions. A first one of each of these frame portions is pivotable from the open position into a predetermined or set closed position (as by virtue of suitable stops being provided on the cooperating frame portions) relative to the upper frame section. The second one of each of the frame portions has wheels (idler and/or drive wheels) mounted thereon for engaging the pipeline surface at locations generally opposed to the locations where the drive wheels on the upper frame section engage the pipeline surface thereby, as before, to provide the desired degree of tractive force.
Suitable actuators, as before, are provided for moving the pairs of pivotable frame portions between the open and closed positions. These actuators are arranged to resiliently bias at least the above-noted second ones of the frame portions toward the closed position such that the wheels thereon engage the pipeline surface in pressurized relation thereby to follow irregularities in the pipeline surface and to assist the drive wheels in providing the required tractive force.
The liquid jetting modules are mounted to the frame via their suspension linkages with certain of these modules being mounted to the upper frame section as before. However, the remaining liquid jetting modules are mounted via their respective suspension linkages only to the above-noted first ones of the pivotable frame portions so that when the latter are in their predetermined closed positions (as defined by their respective stops) the positions which the suspension linkages for the liquid jetting modules occupy relative to one another around the pipeline surface are essentially independent of the variable positions of the above-noted second ones of the frame portions as the wheels thereon follow irregularities and/or out of round conditions in the pipeline surface.
By virtue of the above arrangement, the previously noted problems of longitudinal streaking and loss in cleaning efficiencies due to "side stand off" variations are greatly diminished.
Another problem associated with the earlier form of hydrocleaning apparatus described in the above-noted patent applications concerns the mounting arrangement for the several liquid jetting modules. It was previously noted that suspension linkages were used to connect each module to the frame and to permit independent movement of the modules relative to the frame and to one another radially inwardly and outwardly relative to the pipeline when in use. Guide wheels were located on both the forward and rearward portions of each module for contacting the pipeline surface during relative movement therealong. The linkage arrangements as described in the above patent applications are parallel arm linkages and as the modules were moved inwardly and outwardly they were retained in parallel positions relative to the pipeline axis. This arrangement was found to work very well in most situations but in cases where relatively thick pipeline coatings were encountered, it was found that with the forward guide wheel riding up on the relatively thick coating, the minimum standoff distance between the pipeline surface and the rotary swing arm nozzle was excessive at the rear portion of the nozzle pass. While the standoff distance at the forward portion of the pass was acceptable as this was being governed by the front guide wheel, a system had to be found to move the nozzles' rearward pass inwardly towards the pipeline surface so as to permit the normal minimum standoff distance of, for example, one-half inch, to be obtained for the rear pass of each swing arm revolution.
In order to alleviate the above problem the invention in a further aspect provides for a transverse pivot arrangement which secures each module to its associated suspension linkage so as to permit pitching motions of the modules to take place as the guides thereon follow irregularities in the pipeline surface. As a result of this pitching motion, a desired minimum standoff distance between the rotary swing arm nozzles and the pipeline surface can be maintained at both the rearward and forward extremities of the path of motion of the rotary swing arms thus helping to ensure good cleaning efficiencies even in the case of relatively thick coatings.
The transverse pivot described above typically defines an axis passing through the rotation axis of the associated swing arm nozzle assembly. A further desirable feature includes the provision of an adjustment mechanism associated with the pivot to provide for adjustment of the orientation of the nozzle rotation axis in a plane passing through the pivot axis and transverse to the pipeline axis thereby to enable the previously noted side standoff distances to be adjusted an equalized.
Notwithstanding what has been stated above regarding the desirability of providing the transverse pivot for securing each module to its associated linkages, there are situations which may be encountered wherein no pitching or rocking of the modules is desired. Accordingly, as a further feature, means are provided for locking each module relative to a portion of its suspension linkage such that, in use, only the forward guide contacts the pipeline surface with the module moving radially inwardly and outwardly in generally parallel relation to the pipeline surface as the forward guide encounters pipeline surface irregularities, including various coating thicknesses and the like.
In the hydrocleaning apparatus as described in the aforementioned copending applications, the liquid jetting module are positioned on the frame between fore and aft sets of drive wheels. In the course of a hydrocleaning operation it will be appreciated that the high velocity liquid jets are cutting through the coatings with the result being that particles of coatings such as particles of coal tar, large and small pieces of plastic tape and adhesive released from the pipeline surface all tend to become caught under the loaded rear drive wheels with the result being that some of these materials may be pressed back onto the pipeline surface. This phenomenon is called "tabbing" and this material must be scraped off the surface by hand. Also it was noted that strips of the plastic tape tend to get caught in the drive chains and this eventually builds up sufficiently to break the chain.
In order to alleviate the above-noted problem, the present invention in a further aspect provides for all of the drive wheels to be located on the frame such as to be disposed forwardly of the modules and hence forwardly of the region of contact of the liquid jets with the pipeline surface. In this way, the pipeline surface materials (e.g. old coating materials) dislodged by these jets do not interfere with the action of the drive wheels thus avoiding tabbing and fouling of the pipeline surface. Hence, in a preferred embodiment of the invention, the liquid jetting modules and their associated suspension linkages project or extend rearwardly of the hydrocleaning frame assembly in what might be termed a cantilever fashion.
For all forms of hydrocleaning machines some form of protective shrouding is needed, firstly, to prevent injury to personnel due to the ultra high water pressures and rotating equipment involved, and secondly, in order to satisfy environmental concerns. In the operation of the hydrocleaning equipment a mist is created containing liquid and small particles of debris and this must be contained well enough so as not to allow more than perhaps 5% of it or so to escape to the surroundings. The shrouding must be capable of accomplishing the above objectives and, moreover, it must enable the water jetting modules to move radially inwardly and outwardly during operation without possibility of interference between adjacent shrouds.
Accordingly, in a further aspect of the invention, each of the water jetting modules includes a shroud, with the shrouds of adjacent modules being in overlapping relation to one another such that the shrouds together define an annular array surrounding and confining the rotary swing arm nozzles all around the pipeline when in use so as to substantially prevent random escape of liquid and removed debris. The overlapping relationship between the adjacent shrouds allows for substantial radial motions of the liquid jetting modules and their shrouds relative to one another while avoiding both interference between as well as the formation of gaps between the shrouds through which liquid and debris might escape.
In a preferred form of the invention resilient sealing flaps extend between adjacent shrouds in the overlap regions to further inhibit escape of materials from between the shrouds. Certain of the lowermost shrouds are provided with recess means for receiving liquid and debris with an opening being provided for draining liquid and debris from the recess. The shrouds typically include side wall portions which extend toward the pipeline surface into closely spaced proximity thereto to avoid escape of liquid and debris.
It was previously noted that suspension linkages are provided for connecting the modules to the frame with suitable actuators being provided for positively moving these modules toward or away from the pipeline surface. A further improvement concerns the provision of time delays associated with certain of the actuators and arranged to permit the radial movements of the modules to take place in a predetermined sequence which is so selected as to avoid interference between adjacent shrouds during this radial motion either toward or away from the pipeline surface.
In the period when the older pipelines were being constructed, the most common type of pipe coating utilized was coal tar with an outer wrap. The most common outer wrap at the time was asbestos felt. Since 1972, asbestos has been recognized as a hazardous material. Any time this material is present in a working environment, extreme care must be taken to prevent the asbestos from becoming airborne and inhaled by working personnel. Both EPA and OSHA have promulgated regulations concerning such environments.
It is generally accepted that there is no danger to the personnel or environment during application of such an outer wrap because the asbestos is non-friable and encapsulated in tar. However, during the removal process, the condition of the coating is much different. With age, the coal tar and outer wrap become brittle, forming a hard, easily broken coating. In this condition, the asbestos is friable and any mechanical action to the asbestos results in its becoming airborne. Prior methods of removing such coatings included wire brushes, knives, hammers and scrapers. These mechanical techniques each created dust upon removal of the coating, thus rendering these techniques unacceptable under today's safety considerations when there is an asbestos content in the coal tar coating.
Pipeline owning companies are currently confronted with many thousands of miles of pipe coated with asbestos materials without an adequate removal method in existence. Without a safe removal technique, the companies must either lower line pressures, shut down the line or replace it. Development of an approved and safe cleaning and removal technology which complies with environmental and personnel safety standards is therefore greatly needed.
Further features and advantages of the invention will become readily apparent from the following description of a preferred embodiment of same.